The Bouvet triple junction, 20 to 10 Ma, and extensive transtensional deformation adjacent to the Bouvet and Conrad transforms
The Bouvet triple junction, 20 to 10 Ma, and extensive transtensional deformation adjacent to the Bouvet and Conrad transforms
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DOI：
10.1029/1999jb900399
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发表时间：
2000-04-10
影响因子：
3.9
通讯作者：
Carrara, G
中科院分区：
文献类型：
--
作者：
Mitchell, NC;Livermore, RA;Carrara, G
布维三重交界点被认为在 20 Ma 到 10 Ma 之间演化为山脊-断层-断层 (RFF) 类型，将最南端的大西洋中脊 (SMAR) 与布维变换和康拉德变换分别连接到东部和西部。我们使用侧扫和多波束声纳在这两个变换的正北面进行了勘察，该海底最初是在靠近两个变换交界处的 SMAR 处创建的。声纳数据显示，在对板块旋转进行校正后，布维和康拉德两侧的 SMAR 织物彼此平行，因此它们很可能是在同一扩张脊处形成的，并证实三重连接确实是 RFF。我们的第二个主要结果是，SMAR 组构被正断层广泛横切，在沿两个变换测量的 400 公里范围内的大部分地区，以及布维变换以北最强烈的区域。多道地震图像中生长断层和影响沉积物表面的断层表明，变形是长期存在的，并且可能正在持续发生。由于横切断层的方向与剪切带张性裂缝的方向相似，因此我们将这些区域解释为张拉区。这种与主要海洋转变相邻的变形程度是罕见的，我们提出了许多想法来解释其起源。
The Bouvet triple junction has been proposed to have evolved as a ridge-fault-fault (RFF) type between 20 and 10 Ma, connecting the southernmost Mid-Atlantic Ridge (SMAR) with the Bouvet and Conrad transforms, to the east and west, respectively. We surveyed immediately north of these two transforms with side-scan and multibeam sonars, on seafloor that would have originally been created at the SMAR close to its junction with the two transforms. The sonar data reveal that SMAR fabrics on the Bouvet and Conrad sides, when corrected for plate rotation, are parallel to each other, so they were most likely formed at the same spreading ridge and confirm that the triple junction was indeed RFF. Our second major result is that the SMAR fabrics are extensively crosscut by normal faults, over most of the 400 km surveyed along both transforms and most intensely north of the Bouvet transform. Growth faults and faults affecting the sediment surface in multichannel seismic images show that the deformation has been long-lived and is probably ongoing. Since the orientations of the crosscutting faults are similar to those of shear zone tension fractures, we interpret these areas to be transtensional zones. This extent of deformation adjacent to major oceanic transforms is rare, and we develop a number of ideas to explain its origin.